The present invention relates generally to ElectroActive Polymers (EAP) that convert between electrical energy and mechanical energy. More particularly, the present invention relates to polymers and their use as generators for harvesting electrical energy from unused biologically generated energy sources such as the forces generated when a person""s foot contacts a surface during bipedal motion.
In many applications, it is desirable to convert between electrical energy and mechanical energy. Exemplary applications requiring translation from electrical to mechanical energy include robotics, pumps, speakers, general automation, disk drives and prosthetic devices. These applications include one or more actuators that convert electrical energy into mechanical workxe2x80x94on a macroscopic or microscopic level. Common electric actuator technologies, such as electromagnetic motors and solenoids, are not suitable for many of these applications, e.g., when the required device size is small (e.g., micro or mesoscale machines). Exemplary applications requiring translation from mechanical to electrical energy include mechanical property sensors and heel strike generators. These applications include one or more transducers that convert mechanical energy into electrical energy. Common electric generator technologies, such as electromagnetic generators, are also not suitable for many of these applications, e.g., when the required device size is small (e.g., in a person""s shoe). These technologies are also not ideal when a large number of devices must be integrated into a single structure or under various performance conditions such as when high power density output is required at relatively low frequencies.
Several xe2x80x98smart materialsxe2x80x99 have been used to convert between electrical and mechanical energy with limited success. These smart materials include piezoelectric ceramics, shape memory alloys and magnetostrictive materials. However, each smart material has a number of limitations that prevent its broad usage. Certain piezoelectric ceramics, such as lead zirconium titanate (PZT), have been used to convert electrical to mechanical energy. While having suitable efficiency for a few applications, these piezoelectric ceramics are typically limited to a strain below about 1.6 percent and are often not suitable for applications requiring greater strains than this. In addition, the high density of these materials often eliminates them from applications requiring low weight. Irradiated polyvinylidene difluoride (PVDF) when combined with various copolymers is an electroactive polymer reported to have a strain of up to 4 percent when converting from electrical to mechanical energy. Similar to the piezoelectric ceramics, the PVDF-based material is often not suitable for applications requiring strains greater than 4 percent. Shape memory alloys, such as nitinol, are capable of large strains and force outputs. These shape memory alloys have been limited from broad use by unacceptable energy efficiency, poor response time and prohibitive cost.
In addition to the performance limitations of piezoelectric ceramics and irradiated PVDF-based materials, their fabrication often presents a barrier to acceptability. Single crystal piezoelectric ceramics must be grown at high temperatures coupled with a very slow cooling down process. Irradiated PVDF-based materials must be exposed to an electron beam for processing. Both these processes are expensive and complex and may limit acceptability of these materials.
As advances in microchip fabrication continue to reduce the cost and the size of logic devices while increasing their computing capabilities, new portable electronic devices using these logic devices are continually being developed. Also, these logic devices are being incorporated into existing electronic devices to increase their functionality and in some case to enable portability. Cellular phones, pagers, personal digital assistants, MP-3 players, navigational devices and locator devices are a few examples of newer portable electronic devices. These portable electronic devices along with other older portable electronic devices such as flashlights, electric tools, credit card readers and radios are utilized in many activities. All of these devices require a source of electrical energy to operate. Typically, the devices employ disposable or rechargeable batteries as an electrical power source. Performance parameters of the batteries such as cost, weight and life-time are critical element in the design and operation of these devices.
With the portable electronics devices describe above, it would be desirable to reduce or eliminate the need to constantly recharge or replace the batteries that power the devices. One approach to meet this need is to harvest energy from unused biological and environment energy sources. For instance, solar energy may be converted to electrical energy to provide a power source. However, a disadvantage of solar energy is the low energy density of solar power limits the portability solar collectors. Further, solar power does not provide power at night or on cloudy days. Another approach for providing power for portable electronic devices may be to convert unused mechanical energy generated from a biological or an environmental energy source. For instance, a significant portion of the mechanical energy generated while a person is walking is typically unused. In view of the foregoing, alternative devices that efficiently convert unused biological energy sources or unused environmental energy sources to electrical energy would be desirable.
This invention addresses the needs indicated above by providing generators with one or more transducers that use electroactive polymer films to convert mechanical energy to electrical energy. The generators may include one or more transmission mechanisms that transfer a portion of an unused biological energy source, an unused environmental energy source or combinations of both to the one or more transducers located in the generator. The energy received by the transducers may be converted to electrical energy by the transducers in conjunction with conditioning electronics located within the generator. One embodiment of the present invention provides a heel-strike generator integrated into to the heel of footwear to convert mechanical energy generated during human bipedal motion to electrical energy.
One aspect of the present invention provides a generator for converting biologically-generated mechanical energy to electrical energy. The generator may be generally characterized as including: 1) one or more transducers where each transducer comprises at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; 2) conditioning electronics connected to the at least two electrodes and designed or configured to remove electrical energy from the one or more transducers where the conditioning electronics are designed or configured to perform one or more of the following functions: voltage step-up, voltage step-down and charge control; and 3) one or more transmission mechanisms that are designed or configured to receive biologically-generated mechanical energy and to transfer a portion of the biologically-generated mechanical energy to the polymer where the transferred portion of the biologically generated mechanical energy results in a deflection in the portion of the polymer. The biologically-generated mechanical energy may be generated from a biological system selected from the group consisting of a human, animals or both. The polymer may comprise a material selected from the group consisting of silicone elastomers, acrylic elastomers, polyureathanes, copolymers comprising PVDF and combinations thereof. The polymer may be configued in a manner which consists of stacked multilayers to increase active area and thus to increase electrical energy per motion.
The biologically-generated mechanical energy may produce an inertial force or a direct force where a portion of the inertial force or a portion of the direct force is received by the transmission mechanism. In one embodiment, the direct force may be selected from the group consisting of a foot strike, a hand contraction, a hand strike, a finger strike, a chest expansion, a chest contraction and combinations thereof. The inertial force may be from a biologically-generated motion where the one or more transmission mechanisms comprises an inertial mass that is designed or configured to move in response to an inertial force and where the mechanical energy generated by the movement of the inertial mass is used to generate electrical energy. The inertial mass may be part of the device, or it may be an existing mass carried or moved for a different purpose such as a backpack.
In particular embodiments, the generator may include a housing enclosing the one or more transducers and the one or more transmission mechanisms. In some embodiments, the housing may be integrated into footwear. The generator may also include 1) an electrical interface designed or configured to output the electrical energy where the electrical energy is used to power a portable electronic device and 2) one or more batteries for storing electrical energy removed from the one or more transducers where at least one the batteries is used to increase the charge of the polymer.
In particular embodiments, the one or more transmission mechanisms may include a fluid, one or more support members or combinations thereof, designed or configured to transfer the portion of the biologically-generated mechanical energy. The transmission mechanism may includes a fluid- or gel-filled container where the fluid- or gel-filled container is designed or configured to transfer the portion of the biologically-generated mechanical energy. The fluid- or gel-filled container may be a bellows or a bladder.
In yet other embodiments, the generator may include one or more support structures designed or configured to attach to the one or more transducers. The support structures may include a fluid- or gel-filled container where the fluid or gel filled container is designed or configured to deflect one or more portions of a polymer. In addition, the polymer may include a first portion and a second portion arranged in a manner which causes a change in electric field in response to a deflection applied at least one of the first portion and the second portion. In a particular embodiment, one or more sensors may be connected to the generator.
Another aspect of the present invention provides a generator that converts mechanical energy to electrical energy. The generator may be generally characterized as including: 1) one or more transducers where each transducer comprises at least two electrodes connected to the electrical interface and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer and 2) charge control circuitry connected to the at least two electrodes and designed or configured to remove electrical energy from the one or more transducers. The generator may include circuitry to add charge to the polymers at certain times of the cycle. The generator may also include step-down circuitry designed or configured to receive an input signal with an input voltage level and output an output signal with an output voltage level where the output voltage level is lower than the input voltage level. The input signal to the step-down circuitry may be received from the charge control circuitry.
In particular embodiments, the generator may include an electrical output interface designed or configured to output the output signal from the step-down circuitry. The electrical output interface may be connected to a battery or to a portable electronic device. The output voltage level of the output signal may be between about 1.5 Volts and about 48 Volts. The generator may also include one or more power conversion circuitry units designed or configured to reduce the voltage level of a signal within the step-down circuitry. Further, one or more capacitors may reduce a voltage level of a signal received by the one or more power conversion circuitry units
In another embodiment, the generator may include step-up circuitry designed or configured to receive an input signal with an input voltage level and output an output signal with an output voltage level where the input voltage level is lower than the output voltage level. The output signal may be received by the charge control circuitry. Further, an electrical input interface may receive the input signal where the electrical input interface is connected to a battery. A voltage of the battery may be between about 1.5 and about 12 Volts. The step-up circuitry may include a transformer, a transformer primary driver circuit for controlling the transformer.
Another aspect of the present invention provides a generator for converting mechanical energy generated during human bipedal motion to electrical energy. The generator may be generally characterized as including: 1) one or more transducers mounted in footwear where each transducer comprises at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; 2) one or more transmission mechanisms that are designed or configured to receive mechanical energy generated during human bipedal motion and to transfer a portion of the mechanical energy to the polymer where the transferred portion of the mechanical energy results in a deflection in the portion of the polymer and 3) conditioning electronics connected to the at least two electrodes and designed or configured to remove electrical energy from the one or more transducers. Further the conditioning electronics may be designed or configured to perform one or more of the following functions: voltage step-up, voltage step-down and charge control (add and remove charge from the polymer electrodes). The polymer in the transducers may include a first portion and a second portion arranged in a manner which causes a change in electric field in response to a deflection applied to at least one of the first portion and the second portion where the polymer comprises a material selected from the group consisting of silicone elastomers, acrylic elastomers, polyureathanes, copolymers comprising PVDF and combinations thereof.
In particular embodiments, the one or more transmission mechanism may receive mechanical energy when a portion of the footwear contacts a surface during the human bipedal motion. The generator may also include a housing enclosing at least one of the one or more transducers, at least one of the one or more transmission mechanisms and the conditioning electronics. The housing may be water-proof. The generator may also include one or more support structures designed or configured to attach to the one or more transducers.
In a particular embodiment, the footwear includes at least one heel where the one or more transducers, at least one of the one or more transmission mechanisms and the conditioning electronics housing is integrated into the heel of the footwear. The heel may be designed or configured to be detachable from the boot. One or more support members may be mounted in the transmission mechanism where the one or more support members transfer the portion of mechanical energy. Further, one or more support structures may be attached to at least one of the transducers. In a particular embodiment, the one or more support structures are attached to the polymer to form one or more diaphragms.
The transmission mechanism may receive mechanical energy when a portion of the heel contacts a surface during the human bipedal motion. The transmission mechanism may include a fluid- or gel-filled container and where the fluid- or gel-filled container is designed or configured to transfer the portion of the mechanical energy. In particular embodiments, the fluid- or gel-filled container may be a bellows or a bladder. The fluid- or gel-filled container may be designed or configured to contract when the mechanical energy is applied and to uncontract when the mechanical energy is removed where the stroke distance between when the mechanical energy is applied and when the mechanical energy is removed is between about 1 mm and about 10 mm.
Another aspect of the present invention provides a generator for converting environmentally-generated mechanical energy to electrical energy. The generator may be generally characterized as including one or more transducers where each transducer comprises at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; 2) conditioning electronics connected to the at least two electrodes and designed or configured to remove electrical energy from the one or more transducers; and one or more transmission mechanisms that are designed or configured to receive environmentally-generated mechanical energy and to transfer a portion of the environmentally-generated mechanical energy to the polymer wherein the transferred portion of the environmentally generated mechanical energy results in a deflection in the portion of the polymer. The environmentally-generated mechanical energy may be generated from an environmental energy source selected from the group consisting of wind, waves and water flow.
In one aspect, the present invention relates to a device for converting between electrical energy and mechanical energy. The device comprises at least one transducer. Each transducer comprises at least two electrodes and a polymer in electrical communication with the at least two electrodes in a manner that supports one of electrical generation and mechanical actuation. The device also comprises a first member having a proximate end coupled to a first region of the transducer and a distal end. The device additionally comprises a second member having a proximate end coupled to a second region of the transducer and a distal end coupled to the distal end of the first member. Deflection of the polymer along a plane causes the proximate ends of the first and second members to translate along the plane and causes said distal ends of the first and second members to translate together in a direction that is not coplanar with the plane.
These and other features and advantages of the present invention will be described in the following description of the invention and associated figures.